In general, heating elements are classified into linear, planar and liquid heating elements. A linear heating element is comprised of nichrome wire placed at regular intervals and mounted inside a heating apparatus, such as an electric heat mat. Korean Patent Publication No. 96-7905 discloses a carbon fiber based linear heating element for use in an electric heat mat. The disclosed heating element comprises a conductive part made out of an extremely thin carbon fiber, an insulator covering the conductive part and a coating layer, such as silicon, having superior heat resistance and applied on the outer surface of the insulator.
A planar heating element consists of a heating material coating which is applied on an entire surface of an electric heating apparatus having a predetermined area and generates heat when electric power is supplied. For example, such a planar heating element can be prepared by uniformly coating fine ceramic particles and conductive carbon particles on a fabric cloth using a computer device and polymerizing the coated particles. Korean Patent No. 356309 discloses a planar heating element having a conductive layer with a silk-screen printed conductive ink, which can ensure constant heat generation for providing a highly reliable heating product. This patent eliminates a process of sewing a copper plate on a fabric cloth and prevents nonuniformity of a resistance caused due to failure to uniformly coat the carbon particles on the fabric cloth.
Planar heating elements are recognized as high tech new materials that cause substantially no danger or functional problem in electric products, as compared to conventional linear heating elements using nichrome heating wire.
While many linear and planar heating elements have been developed, liquid heating elements have not been actively studied or developed. Only techniques relating to a heater or heating element that generates its own heat without flame by an exothermic chemical reaction and a heating container (hot can) utilizing the same are known with respect to liquid heating elements. U.S. Pat. Nos. 5,609,786, 5,465,707, 5,205,277 (EP 0564680A), U.S. Pat. Nos. 4,809,673 and 4,559,921 and Korean Patent Publication Nos. 2000-199720, 1995-7752 and 199424131 disclose the hydration reaction of CaO for generating heat in a heating container. U.S. Pat. No. 4,949,702 and Korean Patent Publication Nos. 1994-1060 and 1987-10838 disclose a self-heating container having a metal oxide heater therein Also, U.S. Pat. Nos. 5,018,505, 5,611,329, 5,443,056, 5,355,869, 5,299,556, 5,220,909, 5,117,809, 4,819,612, 4,522,190 and 4,751,119 and Korean Patent Publication Nos. 2000-198025 and 1998-178091 disclose a heating container using solid metal powder and an oxidizing agent or a liquid reactant.
As stated above, no liquid heating element useful for various heat management systems has been available to date. There is an increasing demand for such a liquid heating element.